Shrew opossum

Shrew opossums Temporal range: Late Oligocene–Recent PreЄ Є O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Class:	Mammalia
Infraclass:	Marsupialia
Order:	Paucituberculata Ameghino, 1894
Family:	Caenolestidae Trouessart, 1898
Genera
Caenolestes Lestoros Pliolestes (†) Pseudhalmarhiphus (†) Rhyncholestes Stilotherium (†)

The order Paucituberculata /ˌpɔːsᵻˌtjuːbərkjᵿˈlɑːtə/ contains the seven surviving species of shrew opossum: small, shrew-like marsupials that are confined to the Andes mountains of South America.^[1] The order is thought to have diverged from the ancestral marsupial line very early. Traditionally, they have been considered part of Ameridelphia alongside true opossums, but genetic studies indicate a closer relationship to australidelphians.^[2][3] As recently as 20 million years ago, at least seven genera were in South America. Today, just three genera remain. They live in inaccessible forest and grassland regions of the High Andes.

Shrews were entirely absent from South America until the Great American Interchange three million years ago, and are currently present only in the northwestern part of the continent. Traditionally, it was thought that shrew opossums lost ground to these and other placental invaders that fill the same ecological niches. Evidence suggests, however, that both groups not only overlap, but do not seem to be in direct competition, and the marsupials' larger size seems to imply that they prey on shrews and rodents^[4] Several opossums, such as Monodelphis, also occupy small insectivore niches.

Shrew opossums (also known as rat opossums or caenolestids) are about the size of a small rat (9–14 cm long), with thin limbs, a long, pointed snout and a slender, hairy tail. They are largely carnivorous, being active hunters of insects, earthworms, and small vertebrates. They have small eyes and poor sight, and hunt in the early evening and at night, using their hearing and long, sensitive whiskers to locate prey. They seem to spend much of their lives in underground burrows and on surface runways. Like several other marsupials, they do not have a pouch, and it appears that females do not carry the young constantly, possibly leaving them in the burrow.^[5]

Largely because of their rugged, inaccessible habitat, they are very poorly known and have traditionally been considered rare. Recent studies suggest they may be more common than had been thought.

Classification

Within the family of the Caenolestidae, seven species are known:

• Genus Caenolestes
  • Gray-bellied caenolestid, Caenolestes caniventer
  • Andean caenolestid, Caenolestes condorensis
  • Northern caenolestid, Caenolestes convelatus
  • Dusky caenolestid, Caenolestes fuliginosus
  • Eastern caenolestid, Caenolestes sangay^[6]
• Genus Lestoros
  • Peruvian or Incan caenolestid, Lestoros inca
• Genus Rhyncholestes
  • Long-nosed caenolestid, Rhyncholestes raphanurus

However, Bublitz suggested in 1987 there were actually two Lestoros and Rhyncholestes species (those listed here plus L. gracilis and R. continentalis). This is, however, not accepted by most scientists.

References